Drive assemblies for variable torque distribution normally include a differential with an input shaft and two output shafts which have a compensating effect relative to one another. The drive unit for variable torque distribution functions in that, prior to torque being distributed to the two output shafts, part of the torque introduced via the input shaft is branched off the differential carrier. The branched-off percentage of torque is additionally introduced into one of the two output shafts following the branching-off point for the remaining torque. For this purpose, there is provided a transmission stage and a coupling per output shaft. The transmission stage includes an input gear which is driven by the differential carrier and which accelerates or decelerates an output gear. By coupling the output gear to the associated output shaft of the differential, the associated output shaft is accelerated or decelerated. In this way, it is possible, if required, to transmit a greater amount of torque to the one of the two output shafts than to the other one of the output shafts in order to increase the driving stability of the motor vehicle. Such drive assemblies can be used for distributing torque between the two side shafts of an axle differential or for the controlled distribution of torque between the two axle shafts of a central differential of a motor vehicle driven by several axles.
U.S. Pat. No. 6,056,660 describes a drive unit for the driveline of a motor vehicle, which permits an active, i.e. controlled, variable distribution of torque between two output shafts. The drive unit includes a differential drive with a differential carrier and two side shaft gears which are rotatable supported therein and which are driven via differential gears rotating together with the differential carrier. A carrier element carrying a transmission stage is supported on each of the two side shafts. The transmission stage has a plurality of planetary gears which, by way of a first toothed portion, are connected to the differential carrier in a rotationally fast way and which, by way of a second toothed portion engage a sun gear which is firmly connected to the side shaft. Per side shaft, there is provided a multi-plate coupling which, for the purpose of braking a rotational movement of the respective carrier element, have a braking effect relative to the drive housing. In this way, an additional torque is applied to the respective side shaft.
U.S. Pat. No. 5,692,987 proposes a further differential assembly which permits an active torque control between a first and a second output shaft. The differential assembly includes a planetary differential, a transmission stage with a carrier element and two couplings. The couplings are arranged so as to adjoin one another and be supported relative to the stationary drive housing. One coupling serves to brake the carrier element, so that an additional torque is transmitted to the first output shaft. The other coupling serves to brake the first output shaft, so that an additional torque is transmitted to the second output shaft. Overall, the design of the differential assembly is relatively complex.
From DE 103 42 164 A1 there is known a further drive unit for actively controlling the torque in the driveline of a motor vehicle. It includes a differential with a differential carrier which, via a transmission stage, drives two coupling carriers of multi-plate couplings. The transmission stages are designed in such a way that a transfer to high speeds takes place, so that, by closing one of the two couplings, an additional torque can be transmitted to the associated output shaft.
These assemblies are complex and present assembly difficulties. It would be desirable to provide simply designed and easy-to-assembly drive assemblies featuring a variable torque distribution.